Sorption of arsenic species using chitosan based biopolymer sorbent materials

The research focuses on the design and characterization of two- (chitosan/glutaraldehyde) and three-component (chitosan/glutaraldehyde/β-cyclodextrin) biopolymer sorbent materials. The chitosan prepolymer investigated had a low molecular weight (~ 50,000-190,000 gmol-1) and high molecular weight (~ 150,000-375,000 gmol-1) whereas glutaraldehyde was used as the cross linking agent for each biopolymer. Two component chitosan/glutaraldehyde co-monomers were reacted at variable mole ratios (1:15, 1:25 and 1:35). Three-component copolymers containing β-cyclodextrin (β-CD) were obtained by reacting variable mass ratios of β-CD with chitosan (1-3, 1-1 and 1-1/3; chitosan/β-CD (w/w)). The chitosan/glutaraldehyde fraction was held constant at a 1:6 mole ratio comparable to the two-component copolymers. The two- and three-component biopolymer materials were characterized using TGA, FT-IR spectroscopy and elemental analysis (C, H & N). The solid-solution isotherm properties in aqueous solutions for the biopolymers were characterized with two detection methods (UV-Vis and ICAP-OES) with two types of adsorbates, respectively; p-nitrophenol (PNP) and arsenate oxoanion (HAsO4 2-) at alkaline conditions. The Langmuir (i.e. Sips restricted) and the Sips sorption isotherm models were utilized to obtain sorption parameters at pH 8.5 and 295 K, (i.e. surface area estimates, sorption capacities and removal efficiencies) for each biopolymer material. The surface area estimates are as follows for the 1:15, 1:25 and 1:35 chitosan-based two-component biosorbent materials: the Sips restricted values are 46.7, 46.7 and 31.6 m2g-1 and the Sips values are 124, 46.7 and 31.6 m2g-1 for the low molecular weight chitosan material. The Sips restricted are 58.7, 54.2 and 64.7 m2g-1 and for the Sips are 79.8, 64.7 and 96.3 m2g-1 for the high molecular weight chitosan material, respectively. The surface area estimates are as follows for the 1-3, 1-1 and 1-1/3 chitosan and v β-cyclodextrin three-component biopolymer materials: for the Sips restricted are 34.6, 54.2 and 116 m2g-1 and for the Sips are 275, 51.2 and 161 m2g-1, respectively. Removal efficiencies are dependent upon the pH, temperature, and the relative amount of sorbent and sorbate. The removal efficiencies of p-nitrophenol by the biopolymers ranged between 7.1 and 48.9% for low and high molecular weight chitosan biosorbent materials. The removal efficiencies of pnitrophenol by three components, the chitosan, β-cyclodextrin and glutaraldehyde biopolymers ranged between 7.3 and 28.0%. The removal efficiencies of the arsenate oxoanion by the biopolymers ranged between 30.7 and 92.2% for low and high molecular weight chitosan biosorbent materials. The removal efficiencies of arsenate oxoanion by the three-component biopolymers (chitosan, β-cyclodextrin and glutaraldehyde) ranged between 22.8 and 55.4%. The removal efficiencies for the unmodified commercial chitosan (high and low molecular weight) and activated carbon sorbent materials was negligible (~ 0%). The Langmuir (i.e. Sips restricted) and the Sips sorption isotherms both showed similar “best-fit” results for the sorption in aqueous solution data which resulted in neither isotherm model being favoured over the other